Why liars lie: what science tells us about deception

But here's the problem with lying: research shows that the more you lie, the easier it gets, and the more likely you are to do it again.

"The dangerous thing about lying is people don't understand how the act changes us," said Dan Ariely, behavioural psychologist at Duke University.

Lying is in the news this week after US President Donald Trump's longtime lawyer testified that Trump had directed him to pay hush money to a porn star named Stormy Daniels just before the 2016 election. The courtroom admission not only could implicate Trump in a crime, it also potentially exposed months of denials by Trump and his aides as lies.

Why do liars lie?

Psychologists have documented children lying as early as age two. Some experts even consider lying a developmental milestone, like crawling and walking, because it requires sophisticated planning, attention and the ability to see a situation from someone else's perspective to effectively manipulate them. But, for most people, lying gets limited as we develop a sense of morality and the ability to self-regulate.

A 2010 study on the prevalence of lying in the US found that, in a given 24-hour period, most adults reported not telling any lies. Almost half the lies recorded in the study could be attributed to just 5 per cent of participants. And most people avoided lying when they could, turning to deception only when the truth was troublesome.

Harvard cognitive neuroscientist Joshua Greene said, for most of us, lying takes work. In studies, he presented study subjects with a chance to deceive for monetary gain while examining their brains in a functional MRI machine, which maps blood flow to active parts of the brain.

Some people told the truth instantly and instinctively. But others opted to lie, and they showed increased activity in their frontal parietal control network, which is involved in difficult or complex thinking. This suggests that they were deciding between truth and dishonesty – and ultimately opting for the latter.

For a follow-up analysis, he found that people whose neural reward centers were more active when they won money were also more likely to be among the group of liars – suggesting that lying may have to do with the inability to resist temptation.

Scientists don't really know what prevents all of us from lying all the time. Some believe truth-telling is a social norm we internalise, or a result of conflict in our brains between the things we want and the positive vision of ourselves we strive to maintain. But the curious thing about this preventive mechanism is that it comes from within.

"We are our own judges about our own honesty," said Ariely, the Duke psychologist. "And that internal judge is what differentiate psychopaths and non-psychopaths."

External conditions also matter in terms of when and how often we lie. We are more likely to lie, research shows when we are able to rationalise it, when we are stressed and fatigued, or when we see others being dishonest. And we are less likely to lie when we have moral reminders or when we think others are watching.

"We as a society need to understand that when we don't punish lying, we increase the probability it will happen again," Ariely said.

In a 2016 study published in the journal Nature Neuroscience, Ariely and colleagues showed how dishonesty alters people's brains, making it easier to tell lies in the future. When people uttered a falsehood, the scientists noticed a burst of activity in their amygdala. The amygdala is a crucial part of the brain that produces fear, anxiety and emotional responses – including that sinking, guilty feeling you get when you lie.

But when scientists had their subjects play a game in which they won money by deceiving their partner, they noticed the negative signals from the amygdala began to decrease. Not only that, but when people faced no consequences for dishonesty, their falsehoods tended to get even more sensational.

"If you give people multiple opportunities to lie for their own benefit," said Tali Sharot, a cognitive neuroscientist at University College London who led the research, "they start with little lies and get bigger and bigger over time."